Elevators generally operate by means of a pulley-type system. Usually, a cable is attached to the top of an elevator car, and a counterweight is attached to the free end of the cable. The elevator car moves up and down within an elevator shaft when the cable is engaged by a motor. Though this basic system has been used for decades, there are disadvantages inherent in the pulley system method for lifting an elevator. First, the distance that an elevator can travel is limited by the length of the cable. Second, and even more importantly, the method does not maximize efficiency or cost of materials, which is desirable in the construction of green and sustainable buildings.
When an elevator is lifted from the top by means of a cable, the elevator car plays an important structural role in the lifting. The car must be built for strength and stability, so that the elevator car floor is securely attached to the elevator car ceiling, where the cable is attached. On the other hand, if an elevator were lifted from the bottom, the structure of the elevator car would be unimportant. Lighter and economical materials could be used to form the elevator car because the top portion of the car would not need to bear weight. In turn, the motor would not require as much power to lift the elevator. The machine room where the motor is stored in the case of traditional elevators could be eliminated.
Because devices, such as rack and pinion devices or rack and chain devices, have become available for lifting elevators from the bottom, what is needed is an elevator car designed to be constructed from light and economical materials to be utilized with the bottom-driven elevators. One of the specific challenges in creating such a car would be the door. Therefore, what is needed, more specifically, is a door that can function in tandem with such an elevator car. The door and car would need to be lightweight, yet retain the essential function of prior art elevator cars and doors in preventing passengers from falling out of the elevator or reaching into the elevator shaft. The door would also need to open when the elevator arrived at a desired destination, and close before the elevator commenced motion. The door would need some sort of motion sensor system to prevent the door from closing on people or items passing through it. Finally, a car that would allow a door to open on more than one side would allow greater versatility and functionality of the elevator.